Immunoelectron microscopic localization of dystrophin in myofibres

Duchenne muscular dystrophy, a common X-linked recessive human disease, has recently been shown to be caused by the deficiency of a large, low abundance protein called 'dystrophin'^1-2. Biochemical techniques have shown dystrophin to be membrane-associated in skeletal muscle³, with enrichment of dystrophin in the t-tubules of 'triads'^3,4. Other studies using immunohistochemistry on thick (10 μm) sections have shown dystrophin to be located at the periphery of muscle fibres, possibly at the plasma membrane^5-7. These results have been interpreted as being either consistent and complementary⁶, or contradictory⁷. To localize dystrophin more precisely relative to these membrane systems we have employed highly sensitive and spatially accurate immuno-gold electron microscopy of ultra-thin (70-100 nm) cryosections. The major distribution of dystrophin was on the cytoplasmic face of the plasma membrane of muscle fibres, and possibly on the contiguous t-tubule membranes. The presented data, taken together with recently accumulated information regarding the primary structure of dystrophin⁸, suggests that dystrophin is a component of the membrane cytoskeleton in myogenic cells. Thus, myofibre necrosis in patients affected with Duchenne muscular dystrophy is likely the result of plasma membrane instability.